The present invention relates generally to an electronic toll collection (ETC) system, more specifically to an improved tollgate construction capable of preventing multi-path.
In a conventional ETC system, a roadside antenna is installed in a tollgate for performing wireless communication with a vehicle unit and toll collection process against the ID of an IC card installed in the vehicle unit. For this end, the ETC system determines if vehicles passing through the tollgate are ETC vehicles equipped with ETC compatible vehicle units or non-ETC vehicles excluding ETC compatible vehicle units by confirming whether or not wireless communication is established between the roadside antenna of the tollgate and the vehicle units in the vehicles as disclosed in the specification of Japanese patent application no. 11-033340 (or 033340/99).
However, since such conventional ETC system utilizes high frequency such as, for example, 5xc2x78 GHz microwave range for wireless communication between the tollgate and vehicles, it is possible that multi-path occurs in the wireless communication between the tollgate and vehicles because radio wave from the roadside antenna may be reflected by the roof of one of vehicles in a queue or the roof or other structures of the tollgate to reach other vehicles in the queue. Also, there is a possibility where radio wave radiated from the roadside antenna is reflected by the surface of an island and by the roof of the tollgate to cause multi-path between the tollgate and vehicles in adjacent queues.
Under such circumstances, when non-ETC vehicles travel in a particular wireless communication zone, such vehicles should be determined as non-ETC vehicles because no wireless communication is established between the tollgate and the vehicles. However, multi-path may establish wireless communication between the tollgate and other ETC vehicles outside the normal wireless communication zone, thereby making incorrect judgement of the non-ETC vehicles by a vehicle lane control apparatus.
It is therefore an object of the present invention to provide an electronic toll collection system capable of preventing the above mentioned multi-path problems. For this end, the present invention is an electronic toll collection system for automatically collecting toll by wireless communication between a roadside antenna installed in the tollgate and a vehicle unit in each vehicle. It features in covering at least ceiling portion of the wireless communication zone of a tollgate with a radio wave absorbing structure and installing the roadside antenna inside the structure.
Also, the present invention features in covering with radio wave absorbing material the entire or a part of the surfaces of the roof covering the wireless communication zone of the tollgate, side walls, signboards, vehicle detectors, antenna supports, islands and the road adjacent to the wireless communication zone.
Additionally, the present invention features in the provision of an interference radio wave radiation antenna other than the roadside antenna of the tollgate for invalidating any communication by the radio wave leaking outside the vehicle-to-road communication zone.
As a result of the foregoing arrangements, multi-path between the roadside antenna and vehicles traveling outside the communication zone is effectively prevented, thereby maintaining reliability of the ETC system.